Recording medium and recording device

ABSTRACT

A recording disk has a surface provided with guide grooves for controlling the position of a recording head, and recording bits formed in the guide grooves for high-density recording. The recording bits have the shape of a tadpole in a plane. The width Ws of the recording bits is greater than the width Wg of the guide grooves. An AFM probe serving as a recording head travels along the guide grooves without running off the guide grooves. When a tip part of the AFM probe coincides with the recording bit, the tip part drops deep into the guide groove, whereby the recording bit is detected.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a recording medium and arecording device and, more particularly, to a recording disk of 0.5 μmor below in track width or track pitch, and a recording device forrecording information on the recording disk.

[0003] 2. Description of the Related Art

[0004] Recently, computerized society has made remarkable advancementand there has been a demand for the development of techniques thatenables the storage of an increased information volume. Efforts arebeing made in the field of researches into disk type file memories forthe reduction of the diameter of recording bits and the length ofrecording tracks. It is expected that track length for magneticrecording will shrink from its present length of about 2 μm to 1 μm inthe year 2000 and to 0.5 μm or below in the year 2005. A sample servomethod is used for magnetic recording, and a sample servo method usingV-grooves is used for optical recording. The former does not use anyguide grooves, while the latter uses guide grooves, in which recordingbits are formed between the adjacent guide grooves. When tracks of 0.5μm or below in track length or track pitch are used forultrahigh-density recording, the nonrepeatable radial positioning errorin a disk rotating mechanism is large and the sample servo method cannot be used. The recording medium for optical recording has recordingbits formed between the adjacent guide grooves.

[0005] A high-density read-only memory (ROM) using techniques concerningan atomic force microscope (AFM) disclosed in Physical Review Letters,Vol. 56, pp. 930 to 933 (1986) is proposed in Appl. Phys. Lett., Vol.69, pp. 4262 to 4264 (1996). This ROM is formed on a recording diskprovided with recording tracks arranged at a track pitch of 0.1 μm. Therecording disk is not provided with any guide grooves and is providedwith only concave recording bits.

[0006] The conventional recording disks without any guide grooves orthose provided with guide grooves and recording bits formed between theadjacent guide grooves have the following problems.

[0007] When a recording disk of 0.5 μm or below in track length or trackpitch is used for ultrahigh-density recording, a tracking control systemis affected by the nonrepeatable radial positioning error in a diskrotating mechanism. It is said that nonrepeatable radial positioningerror in the operation of a disk rotating mechanism employing ballbearings is about 200 nm, while the same in the operation of a diskrotating mechanism employing liquid bearings is in the range of about 50to 20 nm. Accordingly, it is said that a practical maximum track lengthfor the sample servo system is about 10 times the nonrepeatable radialpositioning error. If track length is 0.5 μm or below the sample servosystem is infeasible and a continuous servo system must be used.

[0008] The guide grooves of a disk having recording bits formed betweenthe adjacent guide grooves, such as a disk for optical recording, areuseless spaces and it is important to eliminate such useless spaces.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of the present invention to solvethe technical problems in the prior art and to provide a recordingmedium that enables tracking of 0.5 μm or below.

[0010] Another object of the present invention is to provide a recordingdevice using the recording medium of the present invention.

[0011] With the foregoing object in view, the present invention providesa recording medium, such as a recording disk, provided with guidegrooves for controlling the position of a recording head, and recordingbits formed in the guide grooves for high-density recording. Thus, therecording disk of the present invention is provided in its major surfacewith guide grooves for controlling the position of a probe (head), andrecording bits formed in the guide grooves, in which the guide groovesare 0.5 μm or below in width and 0.5 μm or below in pitch. The recordingbits may be concave or convex with respect to a direction perpendicularto the guide grooves, and the center of the recording bits may coincidewith the center of the guide grooves, the center of the recording bitsmay be dislocated from the center of the guide grooves, the recordingbits may be different in depth from the guide grooves, and the recordingbits may have a diameter different from the width of the guide grooves.

[0012] The present invention provides also a recording device fordriving the recording medium as mentioned above, provided with a diskrotating mechanism employing ball bearings or liquid bearings.

[0013] A recording device in accordance with the present invention isable to write data to a recording disk according to the presentinvention at a track length of 0.5 μm or below. The recording device isa high-density recording device employing an AFM as a recording head.Lateral forces acting on a probe included in a recording head aremeasured and the probe is controlled by a servocontrol system fortracking control so as to lie on the center of the guide groove. In therecording disk, the width Ws of the recording bits is greater than thewidth Wg of the guide grooves. Therefore, the probe is able to identifythe recording bits through the detection of an atomic forceperpendicularly acting on the probe. The depth of sinking of the probeinto the guide groove when the probe travels along the guide groove isless than that of sinking of the probe into the recording bit. When thedepth of sinking of the probe into the guide groove increases by anincrement corresponding to the difference between the depth of sinkingof the probe into the recording bit and that into the guide groove whenthe probe moves from the guide groove into the recording bit, arecording signal is provided. Thus, information can be erased, andwritten to or read from a desired position without being affected bynonrepeatable radial positioning error even if a conventional drivesystem employing ball bearings or liquid bearings is used, if therecording disk of the present invention is used. The use of therecording disk of the present invention improves the reliability ofultrahigh-density recording.

[0014] The recording disk of the present invention enablesultrahigh-density recording in a high recording density of 1 Tbit (10¹²bits)/in.².

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and other objects, features and advantages of thepresent invention will become more apparent from the followingdescription taken in connection with the accompanying drawings, inwhich:

[0016]FIG. 1A is a fragmentary perspective view of a recording disk in afirst embodiment according to the present invention;

[0017]FIG. 1B are sectional views taken on line a-a′ and on line b-b′,respectively, in FIG. 1A;

[0018]FIG. 2A is a diagrammatic perspective view of a recording devicefor use in combination with the recording disk shown in FIGS. 1A and 1Bfor ultrahigh-density recording;

[0019]FIG. 2B is a sectional view of assistance in explaining theposition of a probe relative to a recording disk;

[0020]FIG. 2C is a sectional view of a disk rotating mechanism employingball bearings;

[0021]FIG. 3 is a diagrammatic view of assistance in explaining atracking control operation and a reading operation;

[0022]FIG. 4A is a sectional view of a recording disk in a secondembodiment according to the present invention provided with guidegrooves having a substantially V-shaped cross section rather than aU-shaped cross section;

[0023]FIG. 4B is a sectional view of a recording disk in a thirdembodiment according to the present invention provided with recordingbits of a depth different from that of guide grooves; and

[0024]FIG. 4C is a sectional view of a recording disk in a fourthembodiment according to the present invention provided with guidegrooves, and recording bits dislocated from the center of guide grooves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Embodiments of the present invention will explained in detail asfollows.

[0026] Referring to FIGS. 1A and 1B, a recording disk 3 has a surfaceprovided with guide grooves 1 for controlling the position of arecording head, and recording bits 2 formed in the guide grooves 1 forhigh-density recording. FIG. 1A is a perspective view of the recordingdevice, and FIGS. 1B are sectional views taken on line a-a′ and on lineb-b′, respectively, in FIG. 1A. The guide grooves 1 are U-shaped. Therecording bits 2 have the shape of a tadpole in a plane. The width Ws ofthe recording bits 2 is greater than the width Wg of the guide grooves1. An AFM probe 6′ (FIG. 2A) serving as a recording head travels alongthe guide grooves 1 without running off the guide grooves 1. The AFMprobe 6′ can be positioned with respect to a radial direction in anaccuracy of 10 nm or below. When a tip part 6 of the AFM probe 6′coincides with the recording bit 2, the tip part 6 drops deep into theguide groove 1 as shown in FIG. 2B, whereby the recording bit 2 isdetected.

[0027] Referring to FIG. 2A, a recording device in a second embodimentaccording to the present invention employs AFM techniques. The recordingdevice comprises an AFM head, a disk rotating mechanism and a controlsystem. The AFM head is provided with the AFM probe 6′ having the tippart 6 and a cantilever arm 7 held at one end thereof, an optical leverdetection system for detecting a force exerted on the tip part 6 of theAFM probe 6′, a recording piezoelectric device 11, and an XYZ scanner 14for controlling the tip part 6. The optical lever detection systemcomprises, as basic components, a laser light source 4, and a positiondetector 5 for detecting a light beam 12. Naturally, the recordingdevice is provided with a rough control mechanism, probeadvancing/retracting mechanism and a probe seek mechanism, which areomitted in FIG. 2A for simplicity.

[0028] Referring to FIG. 2C, the disk rotating mechanism comprises amotor 22, ball bearings and a disk table 31. The stator 37 of the motor22 and the inner rings 33 of the ball bearings are fastened to a shaft38 set on a base 39. A rotor has a cylindrical part 35 of iron fixedlyfitted in the boss of the table 31. The outer rings 32 of the ballbearings and a magnet rotor 36 are mounted on the cylindrical part 35.Balls 34 are held between the outer ring 32 and the inner ring 33 ofeach of the ball bearings. The table 31 is able to rotate. Liquidbearings may be employed instead of the ball bearings. A liquid bearingcan be formed by sealing a liquid between an outer ring and an innerring respectively corresponding to the outer ring 32 and the inner ring33 of the ball bearing. When the disk rotating mechanism is used,nonrepeatable radial position error is in the range of 20 to 200 nm.Highly reliable writing and reading operation can be achieved when therecording disk of the present invention is used in combination with thedisk rotating mechanism of the present invention.

[0029] The recording disk 3 is supported on the table for writing,reading and erasing operations. A controller 20 receives a positionsignal 15, i.e., information about the position of the tip part 6 of theprobe 6′, provided by the position detector 5 upon the detection of alight beam 12, and executes a position control operation, a recordingsignal detecting operation and a write signal generating operation. Thecontroller 20 includes a position control unit 16 which receivesposition information about the position of the tip part 6 of the probe6′, and executes a tracking control operation, and a position controloperation for controlling the three-dimensional position of the tip part6 of the probe 6′.

[0030] If the recording disk 3 is a ROM disk (read-only memory disk),the recording bits 2 are formed in all the guide grooves 1, andinformation is read by detecting the vertical movement of the probe 6′.If the recording disk 3 is a RAM disk (random-access memory disk),address information and system information are read through thedetection of the probe 6′, and information is recorded in data sectionsin which any recording bits 2 are not formed, information is erased, andinformation is read by a small magnetic head formed in the probe 6′. Ifthe recording disk 3 is a WORM disk (write-once read-many disk),recording bits are formed in the data section by pressing a probe intothe data sections to form the concave bits using nanoindentations. If anear field optical probe is used instead of the probe 6′, ROMs, RAMs andWORMs can be realized. The probe 6′ may be mounted on a slider.

[0031]FIG. 3 is a diagrammatic view of assistance in explaining atracking control operation when a recording disk provided with guidegrooves 1 of a V-shaped cross section is used. A laser beam 12 reflectedby the back surface of the cantilever arm 7 falls on the positiondetector 5 having four photodetectors. The position detector 5 may besuch as provided with photodetectors arranged in a two-dimensionalarrangement. When the probe 6 is twisted by the guide groove, a lateralforce (horizontal force) acts on the probe 6. This lateral force isdetermined by operating the output signals of the four photodetectors ofthe position detector 5 so as to determine a twisting direction. Thus, alateral signal as shown in FIG. 3 is produced. The output signal of theposition detector 5 is positive when the tip part 6 of the probe 6′moves in one direction from the center of the guide groove and isnegative when the tip 6 of the probe 6′ moves in the opposite directionfrom the center of the guide groove. This characteristic of the outputsignal of the position detector 5 is substantially linear when the tippart 6 of the probe 6′ moves in the guide groove. The deviation of thetip part 6 of the probe 6′ from the center of the guide groove isdetermined as the variation of the lateral force, the XYZ scanner 14 iscontrolled so as to keep the tip part 6 of the probe 6′ always on thecenter of the guide groove.

[0032] When the tip part 6 of the probe 6′ come to a positioncorresponding to the recording bit 2, the tip part 6 of the probe 6′sinks further into the recording disk 3, and the depth of sinking of thetip part 6 into the guide groove increases by an increment Δ Z asillustrated in FIG. 2B. The circuit shown in FIG. 3A generates a contactsignal on the basis of the increment Δ Z. Vibrational motions of 10 kHzor below of the probe 6′ are caused by a strain in the recording disk 3.The position control unit 16 controls the XYZ scanner 14 to control theposition of the tip part 6 of the probe 6′ with respect to a directionparallel to the Z-axis so that the tip part 6 of the probe 6′ is incontact with the recording disk 3 at a constant contact pressure. Thecontroller 20 decides that vibrations of the probe 6′ at frequencies of1 MHz or above are information signals, and processes the informationsignals for reading. Thus, information recorded in an ultrahigh densityon the recording disk 3 of the present invention provided with recordingtracks arranged at a track pitch of 0.5 μm or below can be read withoutcausing errors even if a conventional disk rotating mechanism employingball bearings or liquid bearings is used for rotating the recording disk3.

[0033] Recording disks in further embodiments according to the presentinvention will be described below with reference to FIGS. 4A, 4B and 4C.Referring to FIG. 4A, a recording disk 3 in a second embodimentaccording to the present invention is provided with guide grooves 1 of asubstantially V-shaped cross section rather than a U-shaped crosssection. The guide grooves 1 are formed in such a shape when the sameare formed by a conventional process, such as a replica process, anetching process or a lithographic process.

[0034] Referring to FIG. 4B, a recording disk 3 in a third embodimentaccording to the present invention is provided with guide grooves 1 andrecording bits 2 of a depth greater than that of the guide groove 1.This recording disk 3 enables the enhancement of signal intensity, whichimproves the S/N ratio. A recording disk in a modification of therecording disk 3 shown in FIG. 4B may be provided with guide grooves andconvex recording bits of a depth smaller than that of the guide groove.This recording disk can be formed by etching a surface of a disk blankwith regions corresponding to the convex recording bits in the surfaceof the disk blank covered with a resist. The height of the convexrecording bits can be detected more surely than the depth of the concaverecording bits. If the diameter of the concave recording bits is smallerthan that of the tip part of the probe, the tip of the tip part of theprobe is unable to reach the bottom of the recording bits. The convexrecording bits is free from such a problem and hence is capable ofimproving the S/N ratio.

[0035] Referring to FIG. 4C, a recording disk 3 in a fourth embodimentaccording to the present invention is provided with guide grooves 1 andrecording bits 1 dislocated from the center of the guide grooves 1.

[0036] The recording disk may be formed of any suitable material. Inmost cases, the recording disk is formed of an organic material, such asa polycarbonate resin. The surface of the recording disk may be of amultilayer structure, and the bottom wall of the guide grooves and theside walls of the guide grooves may be formed of other materials,respectively.

[0037] The structure of the recording disk in accordance with thepresent invention may be applied only to the header (address part) andservo region of each sector on a conventional recording disk. Only guidegrooves 1 may be formed in the rest of parts serving as data parts touse the recording disk for ultrahigh-density recording. In such a case,the servo region of a sector needs only a recording bit 2 for a clock.This can be used for write-once erasable recording. For example, whenwriting data to the grooves 1 of the data region of a polycarobonaterecording disk by a force modulation recording method, the recordingpiezoelectric device 11 shown in FIG. 2 is driven to form recording bits2 in the guide grooves 1 by applying pulsed force to the recording disk.The recording disk may be provided with a coating of a magneticrecording material, a magnetooptic material, a phase-changeable materialor an organic dye recording material, and the coating may be coveredwith a protective film.

[0038] The guide grooves may partly be interrupted. The guide groovesmay be formed in concentric circles or in a spiral. A magnetic head or ahead provided with a near field optical probe may be employed instead ofthe AFM probe.

[0039] As is apparent from the foregoing description, according to thepresent invention, ultrahigh-density recording can be achieved with highreliability by a conventional disk rotating mechanism employing ballbearings or liquid bearings and apt to cause nonrepeatable radialpositioning error (NRRE: nonrepeatable run-out error) even if the tracklength or the track pitch of the recording disk is 0.5 μm or below.

[0040] Although the invention has been described in its preferred formwith a certain degree of particularity, obviously many changes andvariations are possible therein. It is therefore to be understood thatthe present invention may be practiced otherwise than as specificallydescribed herein without departing from the scope and spirit thereof.

What is claimed is:
 1. A recording disk having a surface provided withguide tracks formed at a track pitch less than 0.5 μm, and digitalinformation recording parts formed in the guide grooves.
 2. Therecording disk according to claim 1 , wherein the digital informationrecording parts have a concave shape.
 3. The recording disk according toclaim 1 , wherein the digital information recording parts have a convexshape.
 4. The recording disk according to claim 1 , wherein centers ofthe digital information recording parts coincide with a center of theguide grooves.
 5. The recording disk according to claim 1 , whereincenters of the digital information recording parts are dislocated from acenter of the guide grooves.
 6. The recording disk according to claim 1, wherein the digital information recording parts have a depth differentfrom that of the guide grooves.
 7. The recording disk according to claim1 to be used in combination with a recording device using techniquesrelating to probe microscopes.
 8. The recording disk according to claim1 , wherein the digital information recording parts have a diameterdifferent from the width of the guide grooves.
 9. The recording diskaccording to claim 1 , wherein the guide grooves are discontinuous. 10.The recording disk according to claim 1 , wherein the recording disk isformed of a polycarbonate resin.
 11. The recording disk according toclaim 10 , wherein the recording disk has a surface coated with amagnetic material, a magnetooptic material, a phase change material oran organic dye recording material.
 12. The recording disk according toclaim 11 , wherein the recording disk has a surface coated with aprotective film.
 13. The recording disk according to claim 12 , whereinthe guide grooves are formed in a spiral.
 14. The recording diskaccording to claim 12 , wherein the guide grooves are formed inconcentric circles.
 15. A recording device comprising the recording diskaccording to claim 9 , and a disk driving mechanism including ballbearings.
 16. A recording device comprising the recording disk accordingto claim 9 , and a disk driving mechanism including liquid bearings. 17.A recording medium comprising a medium having a surface provided withguide grooves for controlling the travel of a probe therein, and digitalinformation recording parts formed in the guide grooves.
 18. Therecording medium according to claim 17 , wherein the guide grooves haveopen ends of 0.5 μm or below in width.
 19. The recording mediumaccording to claim 17 , wherein the guide grooves are arranged at apitch of 0.5 μm or below.
 20. The recording medium according to claim 17, wherein the digital information recording parts have a shape concavetoward the center of the guide grooves.
 21. The recording mediumaccording to claim 17 , wherein the digital information recording partshave a shape convex toward the center of the guide grooves.
 22. Therecording medium according to claim 1 , wherein centers of the digitalinformation recording parts coincide with a center of the guide grooves.23. The recording medium according to claim 17 , wherein centers of thedigital information recording parts are dislocated from a center of theguide grooves.
 24. The recording medium according to claim 17 , whereinthe digital information recording parts have a depth different from thatof the guide grooves.
 25. The recording medium according to claim 17 ,wherein the digital information recording parts have a diameterdifferent from the width of the guide grooves.
 26. The recording mediumaccording to claim 17 , wherein the digital information recording partsare formed in the guide grooves.
 27. The recording medium according toclaim 17 , wherein the recording medium is formed of a polycarbonateresin.
 28. The recording medium according to claim 17 , wherein therecording medium has a surface coated with a magnetic material, amagnetooptic material, a phase change material or an organic dyerecording material.
 29. The recording medium according to claim 17 ,wherein the recording medium has a surface coated with a protectivefilm.
 30. The recording medium according to claim 17 , wherein the guidegrooves are formed in a spiral.
 31. The recording medium according toclaim 17 , wherein the guide grooves are formed in concentric circles.32. The recording medium according to claim 17 , wherein the guidegrooves are discontinuous.
 33. A recording medium comprising a diskhaving a surface provided with guide grooves for guiding a probesupported on a cantilever for traveling along the guide grooves, anddigital information recording parts formed in the guide grooves; whereina laser beam reflected by a back surface of the cantilever opposite afront surface of the same on which the probe is held is measured todetermine a dislocation of the probe from the center of the guide grooveto control the travel of the probe, a distance of shift of the probe ina direction perpendicular to the surface of the disk caused by eachdigital information recording part is measured to read the digitalinformation parts.
 34. A recording medium comprising a disk having asurface provided with guide grooves for guiding a probe, and digitalinformation recording parts formed in the guide grooves; wherein thedigital information recording parts causes the probe to shift in adirection perpendicular to the surface of the disk.
 35. The recordingmedium according to claim 34 , wherein the guide grooves have open endsof 0.5 μm or below in width.
 36. The recording medium according to claim34 , wherein the guide grooves are arranged at a pitch of 0.5 μm orbelow.
 37. The recording medium according to claim 34 , wherein thedigital information recording parts have a shape concave toward thecenter of the guide grooves.
 38. The recording medium according to claim34 , wherein the digital information recording parts have a shape convextoward the center of the guide grooves.
 39. A recording mediumcomprising a disk having a surface provided with guide grooves of U- orV-shaped cross section for guiding a probe for traveling, and digitalinformation recording parts formed in the guide grooves; wherein theguide grooves and the digital information recording parts differ fromeach other in width, a lateral force acting on the probe is detected tocontrol the probe so as to be positioned on the center of the guidegroove, and a distance of shift of the probe in a directionperpendicular to the surface of the disk caused by each digitalinformation recording part is measured.
 40. The recording mediumaccording to claim 39 , wherein the guide grooves have open ends of 0.5μm or below in width.
 41. The recording medium according to claim 39 ,wherein the guide grooves are arranged at a pitch of 0.5 μm or below.42. The recording medium according to claim 39 , wherein the digitalinformation recording parts have a shape concave toward the center ofthe guide grooves.
 43. The recording medium according to claim 39 ,wherein the digital information recording parts have a shape convextoward the center of the guide grooves.
 44. A recording devicecomprising the recording medium according to claim 39 , and a recordingmedium driving mechanism for driving the recording medium; wherein therecording medium driving mechanism includes ball bearings.
 45. Arecording device comprising the recording medium according to claim 39 ,and a recording medium driving mechanism for driving the recordingmedium; wherein the recording medium driving mechanism includes liquidbearings.